Power on problems on pic16f877a

[heyhey123]

Im having problems in turning on the pic16. Whenever it is connected to peripheral components such as h bridges, ultrasonic sensors and the GPIO pins of the raspberry pi as inputs and outputs, it does not turn on instantly. I still need to turn the vdd on and off before it starts. What can be the problem?

 

[ericgibbs]

Im having problems in turning on the pic16. Whenever it is connected to peripheral components such as h bridges, ultrasonic sensors and the GPIO pins of the raspberry pi as inputs and outputs, it does not turn on instantly. I still need to turn the vdd on and off before it starts. What can be the problem?

hi,
Which type of PIC and is the MCLR pin used/connected?

 

[heyhey123]

hi,
Which type of PIC and is the MCLR pin used/connected?

Im using pic16f877a and the MCLR pin is in series with a 10k resistor then vdd.

 

[ericgibbs]

Im using pic16f877a and the MCLR pin is in series with a 10k resistor then vdd.

hi,
Woops, Sorry I missed the 16F877a line in the Title.!..

If the power supply for the PIC, when the other devices are connected, only rises slowly to the full Vdd then the PIC may not reset at first power up.

You could try adding a low value capacitor from the MCLR pin to 0V, say 10nF or 100nF, keep the 10K connected to Vdd

E

 

[heyhey123]

hi,
Woops, Sorry I missed the 16F877a line in the Title.!..

If the power supply for the PIC, when the other devices are connected, only rises slowly to the full Vdd then the PIC may not reset at first power up.

You could try adding a low value capacitor from the MCLR pin to 0V, say 10nF or 100nF, keep the 10K connected to Vdd

E

Okay thanks! May i ask what the capacitor does to the operation? and should i put resistors on certain outputs? Because when an LED is in parallel with some outputs, such as the hbridge for example, it does not activate as well.

 

[ericgibbs]

Okay thanks! May i ask what the capacitor does to the operation? and should i put resistors on certain outputs? Because when an LED is in parallel with some outputs, such as the hbridge for example, it does not activate as well.

hi,
You always use a series resistor with an LED when driven by a PIC pin.

The capacitor should keep the MCLR low long enough for the main Vdd line to stabilise

 

[heyhey123]

hi,
You always use a series resistor with an LED when driven by a PIC pin.

The capacitor should keep the MCLR low long enough for the main Vdd line to stabilise

Thank you so much for the help sir

 

[KeepItSimpleStupid]

in the 80's, I designed a crane for a model railroad for someone. During design, I was using a linear supply and sometimes the processor would not reset. Later I used a switching supply whose rise-time was pretty quick and I had no problems.

All of the chips were socketed and I notiiced that the RESET pin was driven by a gate. That gate was available in a schmidt trigger version. Once I replaced it, te problem was solved.

I can no longer count the amount of times Verizon has said to turn the power on and off of your modem. An early Westel modem had a power switch. The latter one did not.

I did change things so that my internet Infrstructure is mostly powered by a UPS system except for a repeater. Now, all issues are Verizon;s fault. Including, today's. I suspect that after a planned upgrade this fall, I'll put together a low voltage UPS from a commercial product.

I suspect Eric is spot on. No one uses reset modules because the consume real estate and at one time they were fairly expensive.